3 i2 HEAD AND NECK 



on the upper and posterior part of the lateral wall of the 

 cavity. Its free border begins a little below the centre 

 of the cribriform plate, and passes obliquely downwards 

 and backwards, to a point immediately below the body 

 of the sphenoid, where it ends. The middle concha (Fig. 

 1 1 6, i 4 ) also is a part of the ethmoid. Its free border begins 

 a short distance below the anterior end of the cribriform 

 plate, and at first takes a vertical course downwards ; then, 

 bending suddenly, it passes backwards, and it ends midway 

 between the body of the sphenoid and the posterior border 

 of the hard palate. The inferior concha (Fig. 1 1 6, 15) is an 

 independent bone ; it extends backwards, upon the lateral 

 wall of the nasal cavity, midway between the middle concha 

 and the floor of the nose. Its lower free margin is some- 

 what convex downwards. 



Meatus Nasi. The superior meatus (Fig. 1 16, i 3 ) is a short 

 narrow fissure between the superior and middle conchae. 

 The posterior ethmoidal cells open into its upper and anterior 

 part, by one, or, in some cases, by several apertures. 



To bring the apertures into view, turn the superior concha aside, 

 introduce the blade of a pair of forceps under its entire length, and force 

 it upwards. Care should be taken not to injure the mucous membrane 

 more than is necessary. 



The middle meatus is a much more roomy passage than 

 the superior meatus ; it extends backwards from the atrium, 

 between the middle and inferior conchae. To expose it tilt 

 the middle concha forcibly upwards and backwards. 



The upper and anterior part of the middle meatus leads into 

 a funnel-shaped passage which runs upwards into the corre- 

 sponding frontal sinus. The passage is called the infundi- 

 bulum, and it constitutes the channel of communication 

 between the frontal sinus and the nasal cavity. 



Upon the lateral wall of the middle meatus a deep curved 

 groove or gutter, which commences at the infundibulum and 

 runs from above downwards and backwards, will be seen. 

 The groove is termed the hiatus semilunaris (Fig. 117), and 

 in it are the openings of the anterior ethmoidal cells and 

 the maxillary sinus. The slit-like opening of the maxillary 

 sinus lies in the posterior part of the hiatus semilunaris. 

 The upper boundary of the hiatus semilunaris is prominent 

 and bulging. It is termed the bulla ethmoidalis. On or 



